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Notes from the Field: Hantavirus Pulmonary Syndrome in Visitors to a National Park — Yosemite Valley, California, 2012

On August 16, 2012, the California Department of Public Health announced two confirmed cases of hantavirus pulmonary syndrome (HPS) in California residents who had stayed overnight in Yosemite National Park, launching an investigation by the National Park Service, California Department of Public Health, and CDC. On August 27, Yosemite National Park announced two additional cases, and by October 30, 10 cases had been confirmed.

For this outbreak, a confirmed case was defined as detection of 1) a febrile illness and hantavirus (Sin Nombre virus) specific antibodies in serum, or 2) virus antigen in postmortem tissue using immunohistochemistry, in a person who had stayed overnight in Yosemite National Park during June 1–August 28, 2012. CDC notified public health officials and clinical providers in the United States and internationally. The National Park Service notified by e-mail, telephone, or mail all registered overnight Yosemite National Park visitors (approximately 260,000 guests) who had stayed at the park during June 1–September 17, 2012.

The 10 confirmed patients came from three states: California (eight), West Virginia (one), and Pennsylvania (one). Ages ranged from 12 years to 56 years; four were female. Nine patients had typical symptoms of HPS, and one lacked respiratory symptoms; three died.

Nine patients stayed in Curry Village "signature" cabins, which have insulation between the canvas exterior and interior hard walls. Rodent infestations were detected in the insulation, and all 91 signature cabins were closed indefinitely on August 28. In addition, educational interventions were enhanced for staff members and visitors parkwide, and multifaceted rodent control measures, including trapping throughout Curry Village, were implemented.

HPS is a nationally notifiable disease caused in the United States most commonly by Sin Nombre virus. The deer mouse (Peromyscus maniculatus) is the reservoir. Infected mice shed virus in urine, feces, and saliva. Humans become infected through inhalation of aerosolized virus from rodent excreta and via direct contact from rodent bites. The incubation period ranges from 1 to 6 weeks. Early symptoms include fever, chills, myalgia, headache, and gastrointestinal symptoms for 1–7 days, progressing rapidly to respiratory distress and shock (1). Most patients require hospitalization, supplemental oxygen, and intubation. The case-fatality rate is approximately 36% (2). There is no specific treatment for HPS, but early supportive care can reduce mortality (2). Before this outbreak, 58 cases of HPS had been reported among California residents since 1994; two had been visitors to Yosemite National Park before 2012 (California Department of Public Health, unpublished data, 2012).

Clinicians are reminded to consider the diagnosis of hantavirus infection in all persons with febrile illness and sudden onset of respiratory symptoms with a history of rodent exposure. Because HPS is a reportable disease in the United States, clinicians suspecting HPS should notify and consult their state health department about confirmatory testing. More information is available from CDC regarding hantavirus clinical assessment, treatment and diagnostics (3). Park visitors and the public are advised to avoid contact with rodents and their urine, droppings, and nesting materials.

CDC. Hantavirus. Atlanta, GA: US Department of Health and Human Services, CDC; 2012. Available at http://www.cdc.gov/hantavirus. Accessed November 14, 2012.

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